The invention involves an implant as a bone replacement (endoprosthesis), having a base structure with a surface at least partially covered by an open-meshed, three-dimensional structure constructed from particles having four to eight studs extending radially outward from each other, at least three of the studs being directly connected to the base structure.
Such an implant is obtained, for example, by the performing the process according to German patent DE-C 41 06 971 (U.S. Pat. No. 5,178,201). An implant of this type has proven itself in recent years to be excellent, especially in regard to the planned growth into and through the three-dimensional, open-meshed structure, which at least partially covers the surface of the implant.
The growth penetration behavior of the implant can be further improved in that, according to German patent DE-C 42 08 247 (U.S. Pat. No. 5,433,750), several discrete zones having different mesh widths are generated on the surface of the implant. In the process, the mesh widths are adapted to the cellular nature and porosity of the bone material which is in contact with the surface structure of the implant after its implantation. This adaptation is in the sense that the respective mesh widths of the zones correspond approximately to the sizes of the cells and pores of the natural spongiosa, which should grow into and onto, or penetrate through, the surface structure of the implant.
As mentioned, known implants have proven themselves excellently in practice. They have a property though, which becomes noticeable in a negative way during a revision operation, i.e. when removing the implant which has grown affixed to the surrounding spongiosa material. Thus, the surface structures of the known implants are, in particular, constructed in such a jagged manner that a removal of the bone trabecula which has grown into the material is not readily possible using a suitable tool, since the tool frequently hooks onto the deeply-indented surface. This disrupts the progress of the revision operation in an undesirable way.